Knee joint replacement apparatus

ABSTRACT

During the course of a total knee replacement, at least one and preferably a number of different low friction members having rotated artificial surfaces of different rotated angles are provided in order to determine the appropriate angle and displacement of the aritificial prominence and plateaus on the low friction members, so that the appropriate low friction member may thereafter be permanently installed during the total knee replacement in order to recreate the optimal position.

BACKGROUND OF THE INVENTION

The present invention relates generally to apparatus and related methodsfor repairing or replacing deteriorated joints, and is especiallyadapted for use in repairing or replacing the human knee joint.

The joint of the human knee is formed by the low friction and movablecontact between the femur (thigh bone) and the tibia (shin bone). Theupper extremity of the tibia has a surface defined by a generallycentrally located prominence, referred to as the intercondular eminence,extending generally longitudinal in the direction of joint motion, theeminence fitting within a corresponding groove in the distal femur. Thetibial bearing surface includes a pair of tibial plateaus on oppositesides of the longitudinal eminence which are adapted to act as bearingsurfaces for the two ball-shaped bearing surfaces on opposite sides ofthe femoral groove, called the "femoral condyles". The articulations ofthe femur and tibia are held together in a movable relationship by theknee cap (patella), and ligaments and muscles extending both inside andoutside of the knee, with soft fluidic, cushioning tissue extendingbetween the bearing surfaces.

Frequently, a deteriorated knee requires the replacement of the bearingsurfaces of the upper portion of the tibia and the lower portion of thefemur; this is customarily referred to as a "total knee replacement".Because a total knee replacement involves the cutting away of asubstantial portion of the upper portion of the tibia and the lowerportion of the femur and with replacement of those two portions withartificial components, then these artificial components must employ lowfriction surfaces which are capable of cooperating together to simulateas closely as possible the natural movement of the human knee beforesurgery.

A total knee replacement usually involves the removal of approximatelybetween 0.5 to 1.5 centimeters of the upper portion of the tibia,including both the longitudinal eminence and the tibial plateaus,leaving a relatively flat surface into which a rigid metal supportmember is inserted. Then, a low friction bearing member is affixed tothe support member, with the low friction member including alongitudinal prominence simulating the eminence and with bearingsurfaces simulating the tibial plateaus. A lower end portion of thefemur is then removed, and a member having bearing surfaces replicatingthe femoral condyles is then affixed to the remaining end of the femur.

SUMMARY OF THE INVENTION

The present invention is based upon the discovery and observations thatthe rotation of the naturally occurring tibial plateau may not bereplicated in the bearing surface of the artificial low friction member,which may hinder the natural movement of the knee. Accordingly, therehas been devised a method for providing a number of low friction insertmembers having different rotational relationships, so that during thecourse of a total knee replacement, different low friction membershaving rotated artificial surfaces of different rotated angles may beinstalled upon the support member. The knee is then moved through arange of motion to determine the appropriate angle and displacement ofthe artificial prominence and plateaus, and thereafter permanentlyinstalling a member having the appropriate rotational disposition,thereby recreating the optimal position.

Accordingly, the present invention also contemplates a prosthesis forreplacing the proximal aspect of the tibia, with the prosthesiscomprising a member with a low friction surface having a longitudinalprominence designed to simulate and replace the natural eminenceextremity of the tibia. It will of course be understood that thelongitudinal prominence of the bearing member surface is centrallydisposed, with two recessed portions on either side of the prominenceadapted to receive a femoral bearing surface, with the two recessesbeing rotated substantially as the longitudinal prominence of theprosthesis and displaced in an anterior or posterior direction tooptimize correct knee motion.

Generally, the angle of rotation of the longitudinal prominence of theprosthesis is leftwardly for a left knee and rightwardly for a rightknee, with the angle of rotation being on the order of between 3° -15° ,although other rotational displacements may be appropriate in certaincases. It will be understood from the above discussion regarding themethod of the present invention that a number of prostheses withdifferent specific rotational displacements will be provided, so thatthe appropriate rotational displacement can be selected during thecourse of the surgery.

THE DRAWING

FIG. 1 is a perspective view of the top portion of the human tibiabefore a total knee replacement operation.

FIG. 2 is a front elevation of a human tibia after implantation of aprior art total knee prosthesis.

FIGS. 3, 4 and 5 are top plan, front and side views, respectively, of aprior art bearing surface prosthesis like that illustrated in FIG. 2.

FIGS. 6, 7 and 8 are top plan, front and side views, respectively, of atibial bearing surface insert for a left knee in accordance with thepresent invention.

FIGS. 9, 10 and 11 are top plan, rear and side elevations, respectively,of an insert for a right knee in accordance with the present invention.

FIG. 12 is a front view of the tibia and femur after a total kneereplacement using the method of the present invention.

DETAILED DESCRIPTION OF THE DRAWING

A preferred embodiment of the present invention will now be describedwith reference to the drawings.

FIG. 1 illustrates the upper extremity of a human tibia 10, whichincludes a tibial eminence 12. The shape and dimensions of the eminence12 vary, of course, from individual to individual. Nevertheless, theeminence generally extends in a longitudinal direction defined by dottedline 14 between the front and rear of the tibia. A pair of tibialplateaus 16, 18 are positioned on opposing sides of the eminence 12, andare adapted to receive the ball-shaped bearing surfaces at the lowerextremity of the femur (see, for example, the artificial bearingsurfaces 74 and 76 attached to the femur 70 in FIG. 12). The tibialplateaus 16, 20 are defined by an outer peripheral edge 20.

Dotted line 22 in FIG. 1 lies in a plane approximately where a cut istypically made during a total knee operation, in order to remove theupper portion of the tibia 10. Of course, when the upper portion isremoved, the eminence 12, ridge 20 and plateaus 16, 18 are removed aswell. The resulting cut across the plane defined by line 22 generallylies on the order of between 0.5 and 1.5 centimeters below the top ofthe tibia, in the direction of the tibia tubarcle 26. The cut is usuallyflat across the tibia 10. It has been discovered that the longitudinaldirection across the cut at about line 22 results in a significantdisplacement in the longitudinal direction between the front and rear ofthe tibia across the cut, as is illustrated by the dotted line 24. Thisangular displacement is caused by the change in the rotationaldisposition of the tibia downwardly toward the tibial tubarcle 26 fromthe upper extremity of the tibia 10.

In the prior art, as shown in FIGS. 2-5, it has been customary to affixa support member 32 to the cut surface as defined by line 22, with thesupport member 32 having a peg 36 ektending into the tibia 10 to fit theprosthesis to the bone. The surface 34 of the member 32 is dimensionedto receve a low friction member 38. The prior art arrangements for' thelow friction member 38 include a longitudinal prominence 40 whichextends longitudinally front to rear (see FIG. 3), and a pair ofrecessed areas 42, 44 which simulate the tibial plateaus 16, 18 and areadapted to provide a low friction surface for the artificial femurbearing surfaces 74, 76 attached to the femur 70 as part of a total kneereplacement (FIG. 12), As shown in FIGS. 3-5, the prior art bearingmember may include a rear indentation and ridges 43, 45 which surroundthe respective plateaus 42, 44.

Low friction bearing members 50, 50A in accordance with the presentinvention will now be described with reference to FIGS. 6-8 and 9-11,respectively. The arrangement shown in FIGS. 6-8 is designed for usewith a left knee, and the arrangement of FIGS. 9-11 is designed for usewith a right knee. In FIGS. 6-8 and 9-11, common reference numerals areutilized for the same drawing elements.

The perspective bearing member 50, 50A includes a front surface 53, 53Aand a rear surface 55, 55A. An offset longitudinal prominence 52, 52Aextends angularly between the front and rear of the bearing member 50,50A at a respective angular displacement which may be determined duringthe course of a total knee operation, as described in greater detailbelow (or which may determine pre-operatively through the use of CTscanning techniques). That angular displacement is shown by the angulararrow 56, 56A between the longitudinal line 14 and another dotted line54, 54A. Each of the bearing members 50, 50A includes a first recessportion 58, 58A and a second recessed portion 60, 60A designed tosimulate the tibial plateaus 16, 18 of the tibia 10 (FIG. 1). Eachrecessed portion 58, 58A, 60, 60A has a respective ridge 59, 59A, 61,61A surrounding the recess. As noted above, the angular displacementreflected by angle 56, 56A is typically on the order of between about 3°-15° , although other angles may be utilized in certain cases. It iscontemplated that a number of bearing members for a left knee and anumber of bearing members for the right knee having different angularconfigurations would be provided in advance of a total knee operation,so that the surgeon may select the appropriate angular displacementduring the course of the operation. Alternatively, CT scans prior to theoperation may be utilized to define the optimal angle of rotation forthe prosthesis member 50, 50A.

A total knee surgical procedure of course exposes the upper end of thetibia 10. Thereafter, a lateral cut is placed across the top of thetibia 10, generally in the plane of line 22 (FIG. 1), to remove a smallportion of the upper end of the tibia 10 at the knee. The removedportion includes the natural eminence 12 and the bearing surfaces 16, 18for the femoral bearing surfaces. Thereafter, the support member 32 isbe fixed to the cut surface. A prosthesis, such as bearing member 50 inFIG. 12, is temporarily installed upon the support member 32. Thelongitudinal prominence 52 of the bearing member 50 is rotated at asubstantial angle with respect to the longitudinal direction of thetibia 10 across the cut surface 22 as is described above. Afterinsertion of a first bearing member having a particular angulardisplacement for the longitudinal prominence 52, the tibia is then movedto determine knee motion for correctness of the rotation of the angle.If the angle is inappropriate, another bearing member 50 is selected andthe process continued until the proper angular displacement is achieved.Thereafter, the bearing member 50 is permanently installed. As is shownin FIG. 12, it would also be customary to remove a portion of the femur70 including a portion of its natural bearing surfaces, and theinstallation of an artificial femoral bearing surface 72, 74 which isseparated by a groove 80 dimensioned to mate with and receive therotated longitudinal prominence 52.

In a significant number of cases, the rotated longitudinal prominence ofthe present invention will result in a substantial improvement in thefunction of the joint after a total knee operation.

What is claimed is:
 1. A prosthesis for replacing the knee extremity ofa human tibia, the prosthesis comprising a member with an upper lowfriction and a low surface, the upper surface having a longitudinalprominence for replacing the natural eminence of the tibia across theknee extremity, the longitudinal prominence of the prosthesis rotated bya substantial angle with respect to the direction along a line from theposterior of the lower surface to the interior of the lower surface. 2.The prosthesis recited in claim 1, further comprising means for joiningthe member to the tibia after removal of the knee extremity of thetibia.
 3. The prosthesis recited in claim 1 wherein the longitudinalprominence of the upper surface is centrally disposed, the surfacefurther comprising two recessed portions, one portion on either side ofthe longitudinal prominence of the surface, each recessed portionadapted to receive a femoral bearing and being rotated substantially asthe longitudinal prominence of the surface.
 4. The prosthesis recited inclaim 1 wherein the angle of rotation is leftwardly for a left kneeprosthesis and rightwardly for a right knee prosthesis.
 5. Theprosthesis recited in claim 1 wherein the angle of rotation is on theorder of between about 3° -15° .
 6. A method for replacing the upperextremity of a human tibia, comprising the steps of:conducting asurgical procedure to expose the upper end of the tibia; cuttinglaterally across the top of the tibia to remove a small portion of theupper end of the tibia at the knee, including the natural eminence andthe bearing surface for the femoral bearing surfaces; fixing a supportmember across the surface of the cut end of the tibia; providing aplurality of bearing members, each bearing member having a low frictionsurface with a prominence simulating the natural tibial eminence, theprominence of each bearing member positioned at a substantial angle withrespect to the longitudinal direction of the tibia across the cutsurface from the rear of the knee to the front of the knee; temporarilyinstalling one of the bearing members on the support surface; moving thetibia through a knee motion while the one bearing member is temporarilyinstalled to determine the correctness of the angle of the prominence;and thereafter permanently installing one of the bearing members havingthe desired angle of rotation.
 7. The method recited in claim 6 furthercomprising the step of removing a portion of the femur opposite theupper end of the tibia, and affixing a prosthesis to the femur whichappropriately mates with the rotated member installed upon the tibia. 8.The method recited in claim 6 wherein the cutting step comprisesremoving on the order of about 0.5 to 1.5 centimeters of the upper endof the tibia.
 9. A method for repairing a human knee joint by replacingportions of the femur and tibia at the knee comprising the stepsof:cutting an end portion of the tibia including the natural eminenceand the tibial bearing surface which normally contacts with the lowerportion of the femur, and exposing a cut surface of the tibia;installing an artificial member upon the exposed cut surface of thetibia, the artificial member having a low friction surface with anartificial eminence and artificial bearing surfaces, the artificialeminence rotated at a substantial angle with respect to the longitudinaldirection of the tibia across the exposed cut surface from the rear ofthe knee to the front of the knee; removing an end portion of the femurincluding the natural bearing surfaces; and installing a member havingan artificial femoral bearing surface separated by a groove dimensionedto mate with and receive the rotated longitudinal artificial eminence.